package test0; /**
 * Created with IntelliJ IDEA.
 * Description:
 * User: ws
 * Date: 2023-03-28
 * Time: 21:40
 */
import java.util.*;

// https://www.nowcoder.com/practice/1183548cd48446b38da501e58d5944eb?tpId=122&tqId=33662&ru=/exam/oj
public class Main1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int w = scanner.nextInt();
        int h = scanner.nextInt();
        int[][] arr = new int[w][h];
        int count = 0;
        for (int i = 0; i < arr.length; i++) {
            for (int j = 0; j < arr[0].length; j++) {
                if (arr[i][j] == 0) {
                    count++;
                    if (i + 2 < w) {
                        arr[i + 2][j] = 1;
                    }
                    if (j + 2 < h) {
                        arr[i][j + 2] = 1;
                    }
                }
            }
        }
        System.out.println(count);
    }
}
